SoundTrigger DeviceState

- Migrate ST device state listeners to be shared across the service,
  rather than being spawned on demand per-session. Each session
  registers callbacks against the global device state listener.
- Abstract phone state callbacks into separate handler since the
  new telephony callback interface requires registering listeners per
  subscription
- Retain the behavior of only resuming recognition 1s after phone call
  ends via posting a cancellable future
- Add EventLogger for device state events

Bug: 272147641
Fixes: 275105854
Fixes: 267960077
Test: AlwaysOnHotwordDetectionTest - battery state tests
Test: ""#testOnPhoneCall_recognitionPausedAndResumed
Test: Manual verification of battery saver toggle
Test: Manual verification of extreme battery saver toggle
Test: Manual verification of phone call
Test: DeviceStateHandlerTest
Change-Id: Iac5408e7734451fa9399fb09e08184db01b7f9d1